1. Field of the Invention
The present invention relates to a thin-film transistor (“TFT”) substrate and a method of fabricating the same, and more particularly, to a TFT substrate which has improved electrical properties and reduced appearance defects and a method of fabricating the TFT substrate.
2. Description of the Related Art
Liquid crystal displays (“LCDs”) are one of the most widely used flat panel displays (“FPDs”). An LCD includes two substrates having electrodes formed thereon and a liquid crystal layer interposed between the two substrates. In the LCD, voltages are applied to the electrodes to rearrange aligned liquid crystal molecules of the liquid crystal layer and thereby control the amount of light that passes through the liquid crystal layer.
A thin-film transistor (“TFT”) substrate requires active layer patterns, which can supply or block electric charges when power is turned on or off. Currently, hydrogenated amorphous silicon (“a-Si:H”) is widely being used for active layer patterns. Wiring of a TFT substrate using a material with low resistance in order to reduce the signal delay of the TFT substrate is also being considered for active layer patterns.
Disadvantageously, hydrogenated amorphous silicon has a relatively low charge mobility and on/off current ratio. In addition, since hydrogenated amorphous silicon has a small optical band gap, leakage photocurrent is generated from a backlight unit, and an afterimage is created due to an increase in the number of dangling bonds. Consequently, properties of a TFT substrate may deteriorate if active layer patterns of the TFT substrate are made of hydrogenated amorphous silicon.
When an oxide semiconductor is used for active layer patterns and when a material with low resistance is used for data wiring, leakage current and signal delay can be reduced. In this case, however, materials included in the active layer patterns may react with materials included in the data wiring. As a result, defects may occur, such as, for example, where a surface of the data wiring may protrude.